Hydraulic circuits are well known and utilized in a wide variety of machines to articulate linkages and turn motors. A typical hydraulic circuit comprises a hydraulic pump, a spool-type control valve, a double acting hydraulic cylinder, and a hydraulic fluid reservoir. The hydraulic pump draws hydraulic fluid from the reservoir and supplies the fluid to the control valve. The control valve manages the flow of hydraulic fluid from the hydraulic pump to the hydraulic cylinder, and between the hydraulic cylinder and the hydraulic fluid reservoir.
When hydraulic fluid is allowed to flow freely between the hydraulic cylinder and the hydraulic fluid reservoir, the hydraulic cylinder is able to move, or float, in response to external forces acting on it. A float condition may be used in certain situations to conserve energy when lowering a load, exploiting the weight of the linkage to move the hydraulic cylinder, rather than consuming energy to pump hydraulic fluid. During this process, the hydraulic cylinder may be caused to move so rapidly that hydraulic fluid in the hydraulic cylinder cavitates. When this occurs, the rate of hydraulic cylinder movement may become erratic. The resulting erratic movement of load which the hydraulic cylinder supports is undesirable.
A more complete description of the prior art hydraulic circuit illustrated in FIGS. 1-4 is presented in the Detailed Description section of this application.